The objective of this proposal is to continue the development of ultrasonic systems suitable for evaluation of cardiovascular physiology in both animals and human subjects. The primary emphasis will be on developing pulsed doppler ultrasound as a means of measuring blood flow velocity both from implanted transducers and from transducers mounted on the tip of intravascular catheters. These systems will be used to measure flow in chronically instrumented animals and to measure changes in flow velocity in humans particularly in the coronary arterial system of patients undergoing cardiac catheterization and coronary angiography. The second area of ultrasonic development will center around transit time segment length gauges. These transducers are implanted in heart muscle of animals or humans undergoing open heart surgery. The distance between the two ultrasonic crystals is measured on a moment to moment basis and therefore gives an accurate measure of the distance between the two crystals throughout the cardiac cycle. This measurement can be combined with coronary blood flow measurements and left ventricular pressure to give detailed characterizations of regional performance of heart muscle. Major emphasis is placed on evolving a system which ultimately can be used in human subjects.